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United States Patent |
6,085,054
|
Kusayanagi
|
July 4, 2000
|
Wet image forming unit and image forming apparatus
Abstract
A wet image forming unit for developing an electrostatic latent image
formed onto a surface of a photosensitive body by a liquid developing
solution containing toner particles is characterized in that a squeeze
roller for squeezing of a surplus developing solution on the
photosensitive body and cleaning the photosensitive body is provided and,
just before stop of an image forming operation, a voltage whose polarity
is opposite to a charging polarity of the toner particles is applied to
the squeeze roller. The squeeze roller rotates in the direction similar to
the photosensitive body upon the image forming operation. However, just
before the stop of the image forming operation, the squeeze roller rotates
in the direction opposite to the photosensitive body. During printing, the
liquid developing solution which remains and gathers at the interval
between the photosensitive belt and squeeze roller is removed by the
reverse rotation of the squeeze roller not only mechanically, but also
electrically.
Inventors:
|
Kusayanagi; Toshiya (Niigata, JP)
|
Assignee:
|
NEC Corporation (JP)
|
Appl. No.:
|
312977 |
Filed:
|
May 17, 1999 |
Foreign Application Priority Data
| May 18, 1998[JP] | 10-135211 |
Current U.S. Class: |
399/249; 15/256.51 |
Intern'l Class: |
G03G 015/10 |
Field of Search: |
15/256,256.51,256.52
399/233,234,235,237,249
430/117,118
|
References Cited
U.S. Patent Documents
5432591 | Jul., 1995 | Geleynse | 399/249.
|
5576815 | Nov., 1996 | Teschendorf et al. | 399/249.
|
5805963 | Sep., 1998 | Teschendorf et al. | 399/249.
|
Foreign Patent Documents |
54-155843 | Dec., 1979 | JP.
| |
55-137554 | Oct., 1980 | JP.
| |
58-82277 | May., 1983 | JP.
| |
60-28678 | Feb., 1985 | JP.
| |
3-168783 | Jul., 1991 | JP.
| |
6-19266 | Jan., 1994 | JP.
| |
6-314030 | Nov., 1994 | JP.
| |
7-175331 | Jul., 1995 | JP.
| |
8-123207 | May., 1996 | JP.
| |
8-211746 | Aug., 1996 | JP.
| |
8-254932 | Oct., 1996 | JP.
| |
Primary Examiner: Grimley; Arthur T.
Assistant Examiner: Ngo; Hoang
Attorney, Agent or Firm: Ostrolenk, Faber, Gerb & Soffen, LLP
Claims
What is claimed is:
1. A wet image forming unit for developing an electrostatic latent image
formed on a surface of a photosensitive body which rotates in a
predetermined direction by a liquid developing solution containing toner
particles upon an image forming operation, comprising:
a developing roller which develops said photosensitive body surface by said
liquid developing solution;
a squeeze roller for squeezing a surplus developing solution on said
photosensitive body and cleaning, and being arranged on a lower stream
side of said developing roller and rotates in a direction similar to a
rotating direction of the photosensitive body during image forming
operation and rotates in a direction opposite to the photosensitive body
while contacting with the photosensitive body just before stop of the
image forming operation; and
voltage applying circuit which applies a voltage whose polarity is opposite
to a charging polarity of said toner particles to said squeeze roller just
before said stop of the image forming operation.
2. A wet image forming unit according to claim 1, further comprising
a wiper blade for cleaning the liquid developing solution on said squeeze
roller,
wherein said voltage applying circuit applies a voltage whose potential is
the same as that of said squeeze roller to said wiper blade, just before
the stop of the image forming operation and said wiper blade contacts with
said squeeze roller.
3. A wet image forming unit according to claim 2, further comprising a
squeeze roller supporter, wherein after the voltage whose polarity was
opposite to the charging polarity of said toner particles was applied to
said squeeze roller just before the stop of the image forming operation,
said squeeze roller supporter separates said squeeze roller from said
photosensitive body, and said voltage applying circuit applies a voltage
whose polarity is the same as the charging polarity of said toner
particles to said squeeze roller.
4. A wet image forming unit according to claim 3, wherein when said squeeze
roller is separated from said photosensitive body, said voltage applying
circuit applies the voltage whose polarity is the same as the charging
polarity of said toner particles to said wiper blade.
5. A wet image forming unit according to claim 1, wherein upon contacting
with an area which is not used for the image formation of said
photosensitive body, said squeeze roller rotates in a direction opposite
to that upon the image forming operation and cleans.
6. A wet image forming unit according to claim 5, wherein in said
photosensitive body, mechanical intensity of the area used for the
cleaning by said squeeze roller is higher than that of another portion.
7. An image forming apparatus, comprising:
a charging unit which charges a surface of a photosensitive body;
an exposing unit which exposes the charged portion of said photosensitive
body;
a developing unit which develops an electrostatic latent image formed on
the surface of the photosensitive body by said exposing unit by a liquid
developing solution containing toner particles; and
a transfer unit which transfers the developed image by said developing unit
to a paper,
wherein said developing unit comprises:
a developing roller which develops the electrostatic latent image on said
photosensitive body surface by said liquid developing solution;
a squeeze roller for squeezing a surplus developing solution on said
photosensitive body and cleaning, and being arranged on a lower stream
side of said developing roller and rotates in a direction similar to a
rotating direction of the photosensitive body during an image forming
operation and rotates in a direction opposite to the photosensitive body
while contacting with the photosensitive body just before the stop of
image forming operation; and
voltage applying circuit which applies a voltage whose polarity is opposite
to a charging polarity of said toner particles to said squeeze roller just
before said stop of the image forming operation.
8. An image forming apparatus according to claim 7, wherein said developing
unit further comprises a wiper blade for cleaning the liquid developing
solution on said squeeze roller and, just before said stop of the image
forming operation, said voltage applying circuit applies a voltage whose
potential is the same as that of said squeeze roller to said wiper blade
and said wiper blade contacts with said squeeze roller.
9. An image forming apparatus according to claim 8, further comprising a
squeeze roller supporter, wherein after the voltage whose polarity was
opposite to the charging polarity of said toner particles was applied to
said squeeze roller just before the stop of the image forming operation,
said squeeze roller supporter separates said squeeze roller from said
photosensitive body, and said voltage applying circuit applies a voltage
whose polarity is the same as the charging polarity of said toner
particles to said squeeze roller, and when said squeeze roller is
separated from said photosensitive body, said voltage applying circuit
applies the voltage whose polarity is the same as the charging polarity of
said toner particles to said wiper blade.
10. An image forming apparatus according to claim 7, wherein upon
contacting with an area which is not used for the image formation of said
photosensitive body, said squeeze roller rotates in a direction opposite
to that upon the image forming operation and cleans.
11. An image forming apparatus according to claim 10, wherein in said
photosensitive body, mechanical intensity of the area used for the
cleaning by said squeeze roller is higher than that of another portion.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a wet image forming unit for forming a
developed image by using a liquid developing solution containing toner
particles and an image forming apparatus of an electrophotographic system
having the image forming unit, more particularly, to a wet image forming
unit having a squeeze roller for removing a surplus liquid developing
solution from a photosensitive belt and an image forming apparatus.
2. Description of the Prior Art
Hitherto, an image forming apparatus of an electrophotographic system forms
a developed image on a photosensitive body by steps of charging, exposing,
and developing. Further, the developed image is transferred onto a
recording medium by steps of transferring and fixing. As for a developing
solution used in the developing step, there is a liquid developing
solution having dispersing solution with toner particles. A wet image
forming unit using the liquid developing solution forms the developed
image on the photosensitive body to which an electrostatic latent image is
formed.
In the conventional wet image forming unit, the electrostatic latent image
formed on the photosensitive body is developed at an interval between the
developing roller and a photosensitive belt by the liquid developing
solution supplied from a developing solution supply port. Upon this
development, the developing solution adhered to the photosensitive body
excessively is squeezed by a squeeze roller. As a result, the image on the
photosensitive belt is like a film and by a drying step, after that,
transferred to a paper.
In the Official Gazette of Japanese Patent Application Laid-Open No. Hei
8-123207, a squeeze roller is rotated in the direction opposite to the
rotational direction of a photosensitive body during development. As
disclosed in the Official Gazette of Japanese Patent Application Laid-Open
No. Hei 3-168783, a squeeze roller is rotated in the direction similar to
the rotational direction of a photosensitive body during development. In
those squeeze rollers, when the squeeze roller is rotated in the direction
opposite to the photosensitive body during development, there is a fear
that a developed image formed on the photosensitive body by a developing
roller is disturbed and it is difficult that a pressure of the squeeze
roller is set.
Consequently, in view of forming a stable developed image, as shown in the
latter disclosure, it is more preferable that the squeeze roller is
rotated in the direction similar to the rotational direction of the
photosensitive body upon development. In this case, the same voltage
potential as that of the developing roller which supplies a liquid
developing solution to the photosensitive body is applied to the squeeze
roller and, without disturbing the developed image formed by the
developing roller, a surplus developing solution can be squeezed.
However, when the operation to squeeze the surplus developing solution by
the squeeze roller is performed, a part of the surplus developing solution
squeezed from the photosensitive body by the squeeze roller remains and
gathers at an interval (gap) between the photosensitive body and the
squeeze roller, which is located on the upstream side from the center of a
portion where the photosensitive body and the squeeze roller contact. When
the image forming apparatus is stopped while holding this state and left
as it is, the developing solution which is gathering between the gap dries
and congeals. Thus, this exerts a bad influence such that a stain causes
upon next printing or the like.
If a force to press the squeeze roller to the photosensitive body so as to
strongly rub during development is increased, the photosensitive body is
damaged and broken, so that the life is shortened.
The conventional wet image forming unit as mentioned above has a problem
that the liquid developing solution cannot be efficiently removed from the
photosensitive body and the squeeze roller and a bad influence is exerted
upon next printing.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a wet image forming
unit for, just before an image forming apparatus stops, substantially and
effectively removing a liquid developing solution which remains and
gathers at an interval between a photosensitive body and a squeeze roller
which is located on the upstream side from the portion where the
photosensitive body and the squeeze roller contact.
According to the present invention, a wet image forming unit for developing
an electrostatic latent image formed onto a surface of a photosensitive
body by a liquid developing solution containing toner particles is
characterized in that a squeeze roller for squeezing of a surplus
developing solution on the photosensitive body and cleaning the
photosensitive body is provided and, just before stop of an image forming
operation, a voltage whose polarity is opposite to a charging polarity of
the toner particles is applied to the squeeze roller.
The squeeze roller rotates in the direction similar to the photosensitive
body upon the image forming operation. However, just before the stop of
the image forming operation, the squeeze roller rotates in the direction
opposite to the photosensitive body at the contact portion of the roller
and the photosensitive body while contacting with the photosensitive body.
According to the present invention, during printing, the liquid developing
solution which remains and gathers at the interval between the
photosensitive belt and squeeze roller is removed by the reverse rotation
of the squeeze roller not only mechanically, but also electrically.
Therefore, there is an effect such that when the apparatus stops, the
liquid developing solution is substantially and effectively removed from
the photosensitive belt and the squeeze roller.
A wet image forming unit according to the present invention further has a
wiper blade for cleaning the liquid developing solution on the squeeze
roller and a voltage which potential is the same as that of the squeeze
roller is applied to the wiper blade just before the stop of the image
forming operation and the wiper blade contacts with the squeeze roller.
Consequently, the surplus liquid developing solution removed by the squeeze
roller can be efficiently eliminated by the wiper blade.
In a wet image forming unit according to the present invention, after a
voltage whose polarity was opposite to a charging polarity of the toner
particles was applied to the squeeze roller just before the stop of the
image forming operation, the squeeze roller is separated from the
photosensitive body and a voltage whose polarity is the same as the
charging polarity of the toner particles is applied to the squeeze roller.
Hence, the liquid developing solution charging to the opposite polarity
which remains on the surface of the squeeze roller can be perfectly
removed.
In a wet image forming unit according to the present invention, when the
squeeze roller is separated from the photosensitive body, the voltage
whose polarity is the same as the charging polarity of the toner particles
can be applied to the wiper blade.
In a wet image forming unit according to the present invention, the squeeze
roller can clean in an area which is not used for the image formation of
the photosensitive body.
In a wet image forming unit according to the present invention, in the
photosensitive body, mechanical intensity of the area used for cleaning by
the squeeze roller can be higher than that of another portion.
According to the present invention, an image forming apparatus for
developing an electrostatic latent image formed on a surface of a
photosensitive body by a charging unit and an exposing unit by a liquid
developing solution containing toner particles and transferring the
developed image to a paper by a transfer unit is characterized in that a
squeeze roller for squeezing s surplus developing solution on the
photosensitive body and for cleaning the photosensitive body is provided
and just before stop of an image forming operation, a voltage whose
polarity is opposite to a charging polarity of the toner particles is
applied to the squeeze roller. Although the squeeze roller rotates in the
direction similar to the photosensitive body upon an image forming
operation, the squeeze roller, while contacting with the photosensitive
body, rotates in the direction opposite to the photosensitive body at the
contact portion just before the stop of the image forming operation.
According to the present invention, there is provided an image forming
apparatus for developing an electrostatic latent image formed on a surface
of a photosensitive body by a charging unit and an exposing unit by a
liquid developing solution containing toner particles and transferring the
developed image to a paper by a transfer unit by comprising a squeeze
roller for squeezing a surplus developing solution on the photosensitive
body and cleaning the photosensitive body and a wiper blade for cleaning
the liquid developing solution on the squeeze roller. Just before stop of
an image forming operation, the squeeze roller, while contacting with the
photosensitive body, rotates in the direction opposite to the
photosensitive body at the contact portion and a voltage whose polarity is
opposite to a charging polarity of the toner particles to the squeeze
roller. A voltage whose potential is the same as the squeeze roller is
applied to the wiper blade and the wiper blade contacts with the squeeze
roller. Further, after the voltage whose polarity was opposite to the
charging polarity of the toner particles was applied to the squeeze
roller, the roller is separated from the photosensitive body and the
voltage whose polarity is the same as the charging polarity of the toner
particles. When the squeeze roller is separated from the photosensitive
body, a voltage whose polarity is the same as the charging polarity of the
toner particles can be applied to the wiper blade.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic section view of an image forming apparatus of
embodiments according to the present invention;
FIG. 2 is a section view of a wet image forming unit used for the image
forming apparatus in FIG. 1;
FIG. 3 is a side elevation view of the wet image forming unit in FIG. 2 and
showing a state during printing (upper stage of a cam);
FIG. 4 is a side elevation view showing a state just before the wet image
forming unit in FIG. 2 stops printing (middle stage of the cam);
FIG. 5 is a side elevation view showing a state just before the wet image
forming unit in FIG. 2 stops printing (lower stage of the cam);
FIG. 6 is a side elevation view showing a state when the wet image forming
unit in FIG. 2 stops printing (lower stage of the cam);
FIG. 7 is a timing chart showing an operational sequence of the wet image
forming unit in FIG. 2;
FIG. 8A is a side elevation view showing an operation around a squeeze
roller in FIG. 3;
FIG. 8B is a side elevation view showing an operation around a squeeze
roller in FIG. 4;
FIG. 8C is a side elevation view showing an operation around a squeeze
roller in FIG. 5;
FIG. 8D is a side elevation view showing an operation around a squeeze
roller in FIG. 6;
FIG. 9 is a block diagram showing an electric circuit of the image forming
apparatus in FIG. 1; and
FIG. 10 is a top view of a photosensitive belt of the second embodiment.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The embodiments according to the present invention will now be described
with reference to the drawings. FIG. 1 is a whole constructional diagram
showing an image forming apparatus of the embodiments according to the
present invention. The image forming apparatus according to the present
invention prints using an electrophotographic system and is used as
printer, plotter, copying apparatus, facsimile, or the like.
With reference to FIG. 1, a photosensitive belt B is charged by a scorotron
charger 1, exposed by a laser unit 2, and a latent image is formed. The
latent image is developed by a wet image forming unit 3 (as shown by
symbols of 3B, 3C, 3M, and 3Y) using a liquid developing solution of four
colors of yellow, msolutiona, cyan, and black and the developed image is
formed on the photosensitive belt B. The developed image is dried by a
drying unit 4. A liquid developing solution of an ink cartridge 8 is
supplied to each wet image forming unit by a liquid developing solution
circulating pump (not shown). A paper 5 is fed from a hopper 6 and the
image on the photosensitive belt B is transferred by a transfer unit 7. By
the above processes, an image formation is performed. FIG. 1 shows an
example where four wet image forming units 3 (3B, 3C, 3M, 3Y) are used and
a full-color image is formed by toner of four colors of yellow, magenta,
cyan, and black. The present invention is not limited by four colors, but
can be applied to the image formation of a single color or two colors.
As for the liquid developing solution, color powder toner particles
(hereinlater, called toner) of four colors of yellow, msolutiona, cyan,
and black which are dispersed in a dispersing solution.
FIG. 2 is a section view showing the first embodiment of the wet image
forming unit 3 in the image forming apparatus in FIG. 1. FIG. 3 is a side
elevation view of the wet image forming unit 3 and for showing a state
during printing (upper stage of a cam). The section view of FIG. 2 shows a
state where a central portion of a developing roller used by the wet image
forming unit 3 is cut.
With reference to FIGS. 2 and 3, the wet image forming unit 3 according to
the first embodiment has a housing 41, an accumulating chamber 43 for
temporarily holding a liquid developing solution T supplied via a supply
pipe (not shown) from the ink cartridge 8 in FIG. 1, a liquid developing
solution supply port 13 connected to the accumulating chamber 43, a
developing roller 11, a cleaning roller 12, a squeeze roller 14, and a
wiper blade 16.
A connecting pipe 42 is a pipe for returning the liquid developing solution
which has been cleaned and removed by the cleaning roller 12, squeeze
roller 14, and wiper blade 16 to the ink cartridge 8 and for again using
it.
The developing roller 11 develops to an area where the electrostatic latent
image formed on the photosensitive belt B. While developing, the roller 11
rotates in the direction similar to the rotational direction of the
photosensitive belt B. A driven roller 31 rotates while facing to the
developing roller 11. As shown in FIG. 3, the developing roller 11 has a
developing terminal 20 at one end and a developing voltage is applied from
the developing terminal.
The cleaning roller 12 cleans the developing roller 11 while contacting
with the developing roller 11.
The squeeze roller 14 squeezes a surplus developing solution on the
photosensitive belt B during printing and just before the apparatus stops
(that is: before image forming operation stops), it rotates in the
opposite direction and cleans the photosensitive belt B. A rotational
roller 32 is faced to the squeeze roller 14. The wiper blade 16 has a
semiconductive urethane rubber (the resistance value within a range of
1.times.10.sup.4 to 1.times.10.sup.6 .OMEGA.). When the squeeze roller 14
cleans the photosensitive belt B, the wiper blade 16 is pressed to the
squeeze roller 14 and the surplus liquid developing solution squeezed by
the squeeze roller 14 is removed. The wiper blade 16 is held by a blade
holding unit 17. As shown in FIG. 3, a squeeze terminal 15 is connected to
one end of the squeeze roller 14. A voltage is applied to the squeeze
roller 14 and blade holding unit 17 from the squeeze terminal 15.
As shown in FIG. 3, a squeeze supporter 18 supports the squeeze roller 14
and blade holding unit 17. A developing roller supporter 19 supports the
developing roller 11, cleaning roller 12 and the accumulating chamber 43.
The squeeze supporter 18 and developing roller supporter 19 are fixed to a
holding plate 45 which operates in the vertical direction in the housing
41 by rotation of a cam 10.
Therefore, with respect to the developing roller 11 and cleaning roller 12,
and the squeeze roller 14 and wiper blade 16, distances from the
photosensitive belt B can be varied by rotation of the cam 10. But,
position of the driven roller 31 and the rotational roller 32 is
invariable.
Each portion will be described in detail. The developing roller 11 is a
metal cylindrical member and supported rotatably by the developing roller
supporter 19 at the both ends of the developing roller 11. A developing
terminal 20 which is a plate-shaped metal member contacts with the shaft
end portion of the developing roller 11. Upon developing, a developing
voltage is applied to the developing roller 11 from the developing
terminal 20. During developing, the developing roller 11 is arranged at a
position where a minute interval (about 150 [.mu.m]) between the roller 11
and photosensitive belt B is held and is rotated in the direction of an
arrow b in FIG. 3. The liquid developing solution supplied from the liquid
developing solution supply port 13 is conveyed to the minute interval and
the electrostatic latent image formed on the photosensitive belt B is
developed. At this time, an electric field functions between the
developing roller 11 and photosensitive belt B by a voltage applied to the
developing terminal 20 of the developing roller 11 and toner in the
developing solution moves toward the electrostatic latent image of the
photosensitive belt B by electrophoresis.
Movement of toner toward the photosensitive belt B by electrophoresis does
not cause in an area where the electrostatic latent image is not formed.
In this area, although the liquid developing solution adheres to the
surface of the photosensitive belt, the electrostatic adhesion is weak, so
that it can be squeezed by the squeeze roller 14 after development by the
developing roller 11.
Just before the developing operation is finished and the apparatus stops or
after formation of the developed image corresponding to the first sheet,
the developing roller 11 widely separates from the photosensitive belt B.
By contacting with the developing roller 11, the cleaning roller 12 is
rotatably supported to the developing roller supporter 19. As shown in
FIG. 2, the cleaning roller 12 is a cylindrical member whose length is the
same as that of the developing roller 11, substantially. A roller portion
12A is a spongy member. A shaft portion 12B is a metal member whose core
is empty. The shape of the portion to which the roller portion 12A is
attached in the shaft portion 12B is hexagonal. A large number of small
holes are opened on each side of the hexagonal portion. The liquid
developing solution T is supplied to the shaft portion 12B whose core is
empty and supplied to the spongy roller portion 12A from a large number of
small holes of the shaft portion 12B. The cleaning roller 12 is come into
contact with the surface of the outer rim of the developing roller 11 by a
predetermined pressure and rotated in the direction shown by an arrow fin
FIG. 3 upon developing operation. The remaining liquid developing solution
on the developing roller 11 without being developed is cleaned by the
liquid developing solution T oozed from the roller portion 12B.
The squeeze roller 14 is a cylindrical member longer than the developing
roller 11. The roller portion is constructed by a semiconductive urethane
rubber (the resistance value within a range of 1.times.10.sup.4 to
1.times.10.sup.6 .OMEGA.). The shaft portion is constructed by a metal
member whose core is empty and rotatably supported by the squeeze roller
supporter 21 at both ends of the squeeze roller 14. The squeeze roller
supporter 21 is fixed to the squeeze supporter 18.
The squeeze supporter 18 is provided with the wiper blade holding unit 17
for holding the wiper blade 16, the squeeze roller supporter 21, a spring
member 23 having a compressing coil spring 23a and a compressing coil
spring 23b, and a spring bearing 22. The supporter 18 is fixed to the
holding plate 45 via the spring bearing 22. The squeeze roller supporter
21 is fixed to one end of each of the compressing coil springs 23a and 23b
and presses the squeeze roller 14 to the rotational roller 32 by spring
elasticity.
FIG. 9 is a block diagram of an electric circuit system in the image
forming apparatus according to the embodiment of the present invention. In
FIG. 9, a control operation of the whole image forming apparatus is
executed by a control circuit 100. The scorotron charger 1, the laser unit
2 for exposure, a developing roller motor 110, a squeeze roller motor 120,
a wiper blade moving mechanism 130, and switching circuits S1 and S2 are
connected to the control circuit 100, and the above component elements are
controlled, respectively.
The developing roller motor 110 drives the developing roller 11. The
squeeze roller motor 120 drives the squeeze roller 14. The wiper blade
moving mechanism 130 is fixed to the wiper blade holding unit 17 and
allows the wiper blade 16 to contact or separate with/from the squeeze
roller 14 by a predetermined pressure.
The switching circuit S1 is connected to the squeeze terminal 15 in FIG. 3
and switches voltages of +430V, +300V, and -300V of the power source by
the control operation of the control circuit 100. The switching circuit S2
is connected to the developing terminal 20 in FIG. 3, closed by the
control operation of the control circuit 100, and a voltage of +430V is
applied to the developing roller 11.
Subsequently, an operation of the wet image forming unit 3 will be now
described.
FIG. 3 is a side elevation view showing a state during printing; FIG. 4 a
side elevation view showing the first state just before stop of printing;
FIG. 5 a side elevation view showing the second state just before stop of
printing; FIG. 6 a side elevation view showing a state upon stop of
printing; and FIG. 7 a diagram showing an operational sequence of the wet
image forming unit 3. Further, FIGS. 8A to 8D are operational detailed
diagrams around the squeeze roller 14 and FIG. 8A corresponds to a state
in FIG. 3; FIG. 8B a state in FIG. 4; FIG. 8C a state in FIG. 5; and FIG.
8D a state in FIG. 6, respectively.
In the initial state before printing, as shown in FIG. 6, the developing
roller 11 and squeeze roller 14 are separated from the photosensitive belt
B.
If a printing instruction is transmitted to the control circuit 100 in FIG.
9, the photosensitive belt B begins to move in the direction of the arrow
a in FIG. 6 and is charged to +750 [V] by the scorotron charger 1 (in FIG.
1). After that, the liquid developing solution circulating pump (not
shown) begins to move and the liquid developing solution containing toner
charged to the positive polarity on the surface of the developing roller
11 is supplied from the liquid developing solution supply port 13 in FIG.
2. Simultaneously, the switching circuit S2 in FIG. 9 is shut off and a
voltage of +430 [V] is applied to the developing roller 11 and the squeeze
roller 14.
The cam 10 for vertically operating the squeeze supporter 18 and the
developing roller supporter 19 in the wet image forming unit 3 rotates in
the direction of an arrow e in FIG. 6. The squeeze supporter 18 and the
developing roller supporter 19 in the wet forming unit 3 are moved from
the lower stage (the initial position when the apparatus stops, in FIG. 6)
to the upper stage (the position upon printing, in FIG. 3). If the squeeze
supporter 18 and the developing roller supporter 19 (FIG. 3) rises at the
upper stage, the developing roller 11 is arranged at a position where an
interval of 150 [.mu.m] is held from the photosensitive belt B. At this
time, the squeeze roller 14 is pressed to the photosensitive belt B by a
force of 12 [kgf] of the compressing coil springs 23a and 23b in the
spring member 23 set between the squeeze roller supporter 21 and spring
bearing 22.
The exposing process is executed by the laser unit 2 (in FIG. 1) and the
electrostatic latent image is formed on the photosensitive belt B. A
potential of the portion (electrostatic latent image) exposed by a laser
beam is equal to +130 [V] and is remarkably decreased from the potential
of (+750V) of the portion which is not exposed.
By rotating the developing roller 11 in the direction of the arrow b in
FIG. 3, the liquid developing solution T supplied from the liquid
developing supply port 13 is conveyed to the interval between the
photosensitive belt B and developing roller 11. By the electrostatic
latent image which reaches this interval on the photosensitive belt B, an
electric field causes between the photosensitive belt B and developing
roller 11 of +430V and the toner (charged to the positive polarity) in the
liquid developing solution is moved to the electrostatic latent image
portion (portion of +130V) of the photosensitive belt B by electrophoresis
and generates toner developed area. In the portion where the electrostatic
latent image is not formed, the voltage is equal to +750V, so that the
toner charged to the positive polarity is not so moved to the
photosensitive belt B and, inversely, a large quantity of toner is
repulsed from the photosensitive belt B.
In FIG. 3, although during developing, the remaining liquid developing
solution T which is not developed exists on the outer rim of the
developing roller 11, a cleaning process is performed not so as to exert a
bad influence on a next development by the cleaning roller 12 to which the
liquid developing solution T is oozing.
A surplus liquid developing solution is adhered onto the photosensitive
belt B just after development. The surplus liquid developing solution is
both a liquid developing solution which adheres to an area other than the
toner developed area and the dispersing solution of the liquid developing
solution adhered in the developed image.
The surplus liquid developing solution, as shown in FIGS. 3 and 8A, is
squeezed by the squeeze roller 14 pressed to the photosensitive belt B by
a force of 12 [kgf] and the image on the photosensitive belt B becomes
like a film. During development, a voltage of +430V is applied to the
squeeze roller 14 by the switching circuit S1 in FIG. 9 similarly with the
developing roller 11. The toner is electrostatically repulsed so that the
toner in the developed image does not adhere to the squeeze roller 14.
At this time, a part of the liquid developing solution T squeezed by the
squeeze roller 14 is remained and gathered at the interval between the
photosensitive belt B and squeeze roller 14 which is located on the
upstream side from the center contact portion of the photosensitive belt B
and squeeze roller 14.
After that, further, since the image like a film on the photosensitive belt
B needs to be dried, the image is advanced to the drying unit 4 in FIG. 1
and to the transfer unit 7, thereby being transferred to a paper.
When the printing to the control circuit 100 in FIG. 9 by print data is
finished, first, the liquid developing solution circulating pump which
supplies the liquid developing solution T stops and the cam 10 in FIG. 3
rotates in the counterclockwise direction. Thus, the squeeze supporter 18
and developing roller supporter 19 in the wet image forming unit 3 drop
from the position (in FIG. 3) of the upper stage (upon printing) to the
intermediate position (in FIG. 4).
As shown in FIG. 4, when the squeeze supporter 18 and developing roller
supporter 19 come to the intermediate position, the distance between the
squeeze roller supporter 21 and spring bearing 22 is longer than free
length of the compressing coil spring 23a. Hence, in the spring member 23
existing between the squeeze roller supporter 21 and spring bearing 22,
the compressing coil spring 23a does not function. Only the compressing
coil spring 23b having a small spring constant functions and the squeeze
roller 14 is pressed to the photosensitive belt B by a force of 0.9 [kgf].
At this time, the switching circuit S1 in FIG. 9 is switched and, as shown
in FIG. 8B, a voltage (voltage whose polarity is opposite to the charging
polarity (the positive) of the toner contained in the liquid developing
solution T) of -300[V] is applied to the squeeze roller 14 from the
squeeze terminal 15, and the roller 14 rotates in the direction of an
arrow c'. Consequently, during printing, the liquid developing solution T
which remains and gathers at the interval between the photosensitive belt
B and squeeze roller 14 which is located on the upstream side from the
center contact portion of the photosensitive belt B and squeeze roller 14,
is pulled near the squeeze roller side and removed by accompanying with a
squeezing operation. The surface of the photosensitive belt B is cleaned.
In this instance, the wiper blade 16 to which a voltage whose potential is
similar to that of the squeeze roller 14 is applied is pressed to the
outer rim surface of the squeeze roller 14 (in FIG. 8B) . The liquid
developing solution T is also removed from the outer rim surface of the
squeeze roller 14. In the state in FIG. 4, the developing roller 11 and
cleaning roller 12 stop.
Moreover, the cam 10 rotates in the direction of the arrow e in FIG. 4. If
the squeeze supporter 18 and developing roller supporter 19 in the wet
forming unit 3 drop from the intermediate position (upon cleaning, in FIG.
4) to the lower stage (in FIG. 5), the squeeze roller 14 is separated from
the photosensitive belt B. Similarly, the switching circuit S1 in FIG. 9
is switched and a voltage of +300[V] (voltage whose polarity is the same
as the charging polarity of toner particles T' contained in the liquid
developing solution T) is applied to the squeeze roller 14 and wiper blade
16 (in FIG. 8C). As a result, the toner which remains onto the outer rim
surface of the squeeze roller 14 and is charged to the polarity opposite
to the charging voltage of the toner is fully removed by the wiper blade
16 and is cleaned.
After that, the squeeze roller 14 stops rotating. The wiper blade 16 is
separated from the outer rim surface of the squeeze roller 14 by the wiper
blade moving mechanism 130 in FIG. 9. The voltage applied to the squeeze
roller 14 and wiper blade 16 is completely turned off (in FIG. 8D) and,
finally, the photosensitive belt B stops (FIG. 6).
The second embodiment according to the present invention will now be
described. The construction of a wet image forming unit is the same as
that in FIGS. 2 and 3 as mentioned in the first embodiment. FIG. 10 is a
top view and a section view of the photosensitive belt B in the second
invention.
An operation for cleaning the photosensitive belt B by rotating the squeeze
roller 14 in the direction opposite to the moving direction of the surface
of the photosensitive belt B is always executed in the same area as that
without being used for the image formation of the photosensitive belt B.
The area of the photosensitive belt B is mechanically intensified such as
by making the belt thicker than another area. Upon cleaning the
photosensitive belt B, a force which presses the squeeze roller 14 to the
photosensitive belt B is increased (raised from 0.9 [kgf] to 2 [kgf]), and
the liquid developing solution T on the photosensitive belt B is strongly
rubbed and removed.
By the foregoing operations, a voltage applied to the squeeze roller 14 can
be decreased upon cleaning.
As mentioned above, during printing, the same voltage as the developing
voltage is applied to the squeeze roller 14 (in FIGS. 3 and 8A) from the
squeeze terminal 15 of the plate metal member which contacts with the end
of the shaft of the squeeze roller 14. In the spring member 23 of the
compressing coil type between the squeeze roller supporter 21 and spring
bearing 22, both of the compressing coil springs 23a and 23b function and
the squeeze roller 14 is pressed to the photosensitive belt B by a
predetermined force. The squeeze roller 14 is, during printing, driven and
rotated in the direction of the arrow c in FIG. 3 by a frictional force by
the roller 14 and photosensitive belt B and the surplus liquid developing
solution T is squeezed from the liquid developing solution T developed on
the photosensitive belt B.
Just before the apparatus stops after completion of printing, a voltage
different from that during printing is applied to the squeeze roller 14
from the squeeze terminal 15 (in FIGS. 4 and 8B). In the spring member 23
between the squeeze roller supporter 21 and spring bearing 22, only the
compressing coil spring 23b functions, and the squeeze roller 14 is
pressed to the photosensitive belt B by a predetermined force and rotated
in the direction of the arrow c' in FIG. 4. The liquid developing solution
T which is gathered at the interval between the photosensitive belt B and
squeeze roller 14 during printing is removed and the photosensitive belt B
is cleaned.
At this time, the wiper blade 16 to which the same voltage as that of the
squeeze roller 14 is applied from the squeeze terminal 15 is come into
contact with the outer rim surface of the squeeze roller 14. The liquid
developing solution T of the outer rim surface of the squeeze roller 14 is
removed and cleaned. After that, when the squeeze roller 14 is separated
from the photosensitive belt B (in FIGS. 5 and 8C), a different voltage is
also applied to the squeeze roller 14 and wiper blade 16. The liquid
developing solution T is completely removed from the outer rim surface of
the squeeze roller 14.
As described above, the present invention has an effect such that during
printing, a liquid developing solution gathered at the interval between a
photosensitive belt and a squeeze roller is not only mechanically removed
from the surface of the photosensitive belt and squeeze roller, but also
electrically removed and, therefore, when the apparatus stops, the liquid
developing solution is substantially completely removed from the
photosensitive belt and squeeze roller.
An operation for cleaning the photosensitive belt is always performed in
the same area as the area which is not used for image formation, so that
there is an effect such that a voltage applied to the squeeze roller can
be decreased upon cleaning.
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